GOOD DAY...
I'am still a noob when it comes to electronics,so if someone can show me what I'm doing wrong,or missing,I will appreciate it.
Here goes:
Culprit: Laptop charger 19.5v 65w
I am trying to mod this smps so that the CC and CV is adjustable.I have modified other types of smps with no problems...but this one has a dual opamp with v/ref chip (data sheet in attachments) at the output to regulate CV and CC and I can't seem to crack it.(see attachments)
I have made the CV adjustable,but the lower I make the output voltage,the less load I can pull from it before it cuts out.
Things that I have done so far:
1) Took images and revere engineered the circuit.(see attachment)
2) Removed the 4.87k and 499k resistors and replaced them with a 5.6k resistor and 10k multi turn pot in series to make CV
adjustable from 9.8v to 16.8v.
3) Tried to make CC adjustable with multi turn pots at 4.64k resistor with no luck,and then at 115k resistor with no luck as well, then
resoldered resistors back as they were.As soon as I tried to lower the CC it just cuts out,and then saw it even cuts with a small load
at 10v.Basiclly the lower I make the voltage the less load before it cuts out.
4) I then thought its got something to do with the supply voltage at pin 3 in the sens that there is a voltage drop,so changed the 10k
resistor with a 6.8k,no luck and replaced the 10k.
5) I then removed the 1k resistor going to pin 7 to disable the CC completely to rule out that the problem is not from that side and still
no luck,so it must be on the CV regulation side in my opinion.
So I from what I can see is that I'am missing something on operation of opamp 1 with the ref/voltage.
Thanks